1. Field of the Invention
The present invention relates generally to focal-plane shutters, and more particularly to focal-plane shutters having resilient stopping members for absorbing shutter blade impact forces without causing undue wear of the shutter blade connector portions.
2. Description of the Related Art
Japanese Utility Model Publication No. 34892/1981 discloses a known focal-plane shutter in which at least one stopping portion is mounted to a base plate to bring at least some of the closing blades and/or closure-assisting members to a stop. As shown in FIG. 5, a base plate 9 of this structure has bent portions forming stopping portions 9b, 9b which are brought into resilient contact with the front-end surface of a leading blade 6a of a set of closing blades 6a-6e via resilient members 10, 10. Although the stopping portions 9b, 9b are shown to be two in number, at least one stopping portion is provided.
In this known structure, there are provided two stopping portions 9b, 9b in the case shown in FIG. 5. The two stopping portions 9b, 9b are mounted to one side (i.e., the right side) of pivotal portions 7b and 8b which connect the leading blade 6a with closure-assisting members 7, 8 for driving the blade 6a. Therefore, when the leading blade 6a of the set of closing blades 6a-6e is moved by the spring force of a spring (not shown) and collides against the stopping portions 9b, 9b to close the shutter opening 2, the resulting impact forces exert a counterclockwise force on the pivotal portions 7b and 8b. Since this action is repeated each time the shutter is used, eccentric wear occurs on the pivotal portions 7b, 8b, producing rattling between the blade 6a and the pivotal portions 7b, 8b. This makes it impossible to hold the blade 6a stably and, consequently, the exposure accuracy deteriorates.
Furthermore, since the end surface of the blade 6a making resilient contact with the stopping portions 9b, 9b is an end surface that passes over the shutter opening 2 and forms the slit, wear is produced on the end surface that makes resilient contact with the stopping portions 9b, 9b as a result of repeated resilient contacts. As a result, a problem occurs in that the amount of exposure differs between the portions of the end surface of the blade 6a on which wear has occurred and the other non-worn portions, resulting in so-called image nonuniformity.
An object of the present invention is to provide a focal-plane shutter which overcomes the aforementioned drawbacks of prior art shutters.
Another object of the present invention is to provide a focal-plane shutter that prevents the application of unwanted forces to the connector portions connecting the shutter blades to the arms, thereby stabilizing the amount of exposure and improving the durability of the shutter.
A focal-plane shutter according to one embodiment of the present invention comprises a shutter plate having a shutter opening, a set of opening blades for opening and closing the shutter opening, and arms connected via connector portions to the opening blades for driving the opening blades parallel to the shutter opening. Resilient stopping members are provided for making resilient contact with the opening blades at opening positions where the opening blades are in a retracted state and open the shutter opening. The resilient stopping members are plural in number and make resilient contact with the opening blades on opposite sides of the connector portions.
A focal-plane shutter according to another embodiment of the present invention comprises a shutter plate having a shutter opening, a set of closing blades for opening and closing the shutter opening, and arms connected via connector portions to the closing blades for driving the closing blades parallel to the shutter opening. Resilient stopping members are provided for making resilient contact with the closing blades at closing positions where the closing blades close the shutter opening. The resilient stopping members are plural in number and make resilient contact with the closing blades on opposite sides of the connector portions. Since the resilient stopping members make resilient contact with the blades on opposite sides of the connector portions that connect the blades with the arms, impact forces produced when the blades collide against the resilient stopping members cancel out each other at the connector portions. Therefore no extra force acts on the connector portions, thereby enhancing the durability of the shutter.
According to another aspect of the present invention, the set of closing blades makes resilient contact with the resilient stopping members at portions thereof that do not traverse the shutter opening. This prevents damage to the end surface of the slit-forming blade that traverses the shutter opening and forms the slit. Thus the amount of exposure is not altered because of damage to the end surface of the slit-forming blade, even if the closing blades repeatedly collide against the resilient stopping members, thereby maintaining exposure accuracy and improving durability.